Ira Weiny <ira.we...@intel.com> writes: > On Wed, May 20, 2020 at 12:30:57AM +0530, Vaibhav Jain wrote: >> Introduce support for Papr nvDimm Specific Methods (PDSM) in papr_scm >> modules and add the command family to the white list of NVDIMM command >> sets. Also advertise support for ND_CMD_CALL for the dimm >> command mask and implement necessary scaffolding in the module to >> handle ND_CMD_CALL ioctl and PDSM requests that we receive. ... >> + * >> + * Payload Version: >> + * >> + * A 'payload_version' field is present in PDSM header that indicates a >> specific >> + * version of the structure present in PDSM Payload for a given PDSM >> command. >> + * This provides backward compatibility in case the PDSM Payload structure >> + * evolves and different structures are supported by 'papr_scm' and >> 'libndctl'. >> + * >> + * When sending a PDSM Payload to 'papr_scm', 'libndctl' should send the >> version >> + * of the payload struct it supports via 'payload_version' field. The >> 'papr_scm' >> + * module when servicing the PDSM envelope checks the 'payload_version' and >> then >> + * uses 'payload struct version' == MIN('payload_version field', >> + * 'max payload-struct-version supported by papr_scm') to service the PDSM. >> + * After servicing the PDSM, 'papr_scm' put the negotiated version of >> payload >> + * struct in returned 'payload_version' field. > > FWIW many people believe using a size rather than version is more sustainable. > It is expected that new payload structures are larger (more features) than the > previous payload structure. > > I can't find references at the moment through.
I think clone_args is a good modern example: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/sched.h#n88 cheers